Variable direction of view endoscopes allow the user to change the endoscopic viewing direction without having to change the position of the endoscope itself. Such endoscopes are useful when the user wants to see structures which are beside or behind the tip of the endoscope but can not easily move the endoscope shaft because of anatomical constraints or constraints imposed by other surgical instruments in the operative field.
Variable direction endoscopy is desirable because it affords surgeons greater flexibility in their procedural approach. Increased viewing mobility improves the quality of diagnoses, as in cystoscopy for example, where a typical diagnostic screening involves inspecting the interior surface of the bladder for lesions or tumors. The ability to look laterally and retrograde is important when doing this type of diagnosis because it makes it possible to visually cover the entire bladder surface, including the entrance region near the bladder neck. In ear-nose-throat and neurosurgical procedures, variable viewing is desired because the procedures are delicate, and the entrance ports are small. It is therefore not possible to manipulate the endoscope significantly without injuring the patient. The ability to look sideways and backwards is important however during and after tumor resection when it is necessary to keep track of tumor fragments, which if not caught can nucleate new tumors. Laparoscopy, another surgical discipline, imposes fewer maneuvering constraints but still benefits markedly from variable direction viewing because it allows surgeons to get better observation angles during a procedure and increases diagnostic capabilities. Also, because of the greater viewing versatility, variable direction of view endoscopes can minimize conflicts with other tools and can simplify surgical planning by their ability to achieve standard viewing angles from nonstandard positions, allowing the surgeon to keep the endoscope “off to the side” but still get the desired view.
A fundamental feature of variable direction endoscopy is that it generally makes it possible for surgeons to eliminate “blind movements.” A blind movement is the process of moving an instrument inside a patient without being able to see where the instrument is heading. This can occur when it is necessary to advance a fixed-angle side viewing endoscope in its length direction without being able to see what is ahead of the scope, or when a surgical tool has to be manipulated at the boundary of the endoscopic field of view.
Many known variable direction of view endoscopes also have drawbacks. First, these scopes use a movable image sensor or optical element at the tip of the scope to vary the viewing direction. Because of these moving parts, fabricating variable direction of view scopes is complicated and costly, and such scopes are less robust than traditional fixed-angle scopes. Also, they often deliver inferior illumination and image quality.
These scopes, both rigid and flexible tip endoscopes, also subject the user to disorientation. As the endoscopic line of sight is changed, the user faces two difficulties. The first is keeping track of where the endoscope is “looking.” With a rigid fixed-angle endoscope it is relatively easy for the user to extrapolate the endoscopic viewing direction from the position of the endoscope shaft. This is not the case when the viewing direction is regularly changed relative to the longitudinal axis of the endoscope; the user quickly loses track of spatial orientation within the anatomy being observed. The second difficulty is keeping track of what is “up” in the endoscopic image. Depending on the view-changing mechanism, the image will rotate relative to the surroundings, and the user frequently loses orientation. This disorientation is often not correctable, especially in variable direction of view scopes which have distal imagers and no facility for changing image orientation.
Given the difficulties of variable direction endoscopes, it is common for surgeons to utilize rigid endoscopes with fixed viewing angles. Surgeons rely heavily on knowing that a certain endoscope provides a 30 or 45 degree viewing angle. This preference for using multiple fixed angle endoscopes is due in part to the fact that a surgeon knows that for a particular endoscope they can dependably know what the anatomy should look like. FIGS. 1A, 1B, 1C and 1D show the distal ends of four commercially available endoscopes 10, 20, 30, 40 with the most commonly used viewing directions (view vectors) 50 corresponding to angular offsets from the longitudinal endoscope axis 60 of 0, 30, 45, and 70 degrees. Different surgical procedures typically require endoscopes of most of these angles with specific emphasis on one of them, often the 30 degree endoscope because it provides both a good forward view and a certain amount of lateral viewing. However, in most procedures, such as ear-nose-throat, bladder, orthopedic, brain, and abdominal procedures, lateral and partial retroviewing is beneficial and can be vital. Unfortunately surgeons often try to make due with only one or two scopes because changing the endoscope mid procedure is cumbersome (both light and camera cables have to be disconnected and reconnected), time consuming, and sometimes dangerous. Also, inserting off-angle endoscopes can be dangerous because they are not “looking” in the direction they are being inserted. This is a problem in neurosurgery, where surgeons often will not use 45- or 70-degree endoscopes because they are afraid of blindly thrusting the endoscope into delicate tissue.
Several designs have been proposed that provide solid state variable direction of view endoscopes to reduce or eliminate the number of moving parts. U.S. Pat. Nos. 5,185,667 and 5,313,306 disclose using a fish-eye lens that provide a hemispherical field of view, i.e. the lens provides a wide angle image that provides variable viewing in both the x and y directions. U.S. Pat. No. 6,449,103 discloses the use of an endoscope with a catadioptric system. U.S. Pat. No. 5,800,341 discloses an endoscope with charged coupled devices (CCDs) forming a circumferential band about the distal portion of the endoscope or CCDs covering substantially all of the outer side wall of the shaft adjacent to the distal end. U.S. Pat. No. 5,954,634 discloses the use of an image sensor at the proximal end of the endoscope that can move in a direction perpendicularly to the optical axis to enable selected portions of the image field to be viewed. However, these solutions can be considered deficient because they either provide poor resolution compared to a standard 70 degree field of view system, are overly complex and not feasible to manufacture, do not provide retrograde viewing, i.e. viewing at an angle greater than 90 degrees relative to the axis of the endoscope in the distal direction, or still incorporate overly complex motion.
What is desired, therefore, is variable direction of view endoscope that can provide a feasible design and reduce the number of moving parts. It is further desired to provide an endoscope that can also provide forward and retrograde viewing. It is still further desired to provide an endoscopic system that enables a surgeon to utilize reliable standard endoscopic viewing angles and at the same time provide an overall field of view that encompasses the viewing range.